The present invention relates to blood gas monitoring. More particularly, the present invention relates to a probe used in a system for monitoring blood gases from an artery.
As a person inhales air from the atmosphere, the air enters the alveoli in the lungs. Since the human body utilizes oxygen and expels carbon dioxide, the concentration of oxygen in the air inhaled by a person into the alveoli is higher than the concentration of oxygen in the arterial blood stream. In addition, the concentration of carbon dioxide in the blood stream is higher than the concentration of carbon dioxide in the inhaled air. Thus, according to the law of partial pressure, oxygen diffuses from the lungs, across the alveoli into the bloodstream, and carbon dioxide diffuses from the bloodstream across the alveoli into the lungs. The oxygen is then carried by the bloodstream to the remainder of the body. The carbon dioxide is exhaled from the lungs and therefore expelled by the body.
Due to this interaction, the concentrations of carbon dioxide and oxygen in the blood can give a physician useful diagnostic and treatment information. In short, by measuring arterial blood gases such as oxygen and carbon dioxide, the treating physician can get, among other things, some indication of how well the heart and lungs are operating.
This has given rise to a number of conventional blood gas monitoring techniques. In one conventional blood gas monitoring system, a blood sample is removed from the patient and transported either to a laboratory or to a bed-side analyzer for analysis. The blood sample is analyzed to determine the levels of blood gas in the blood sample drawn from the patient.
A second method is also known for monitoring blood gas. In the second method, a blood gas probe is inserted into the artery. Blood gas is allowed to diffuse across a membrane and is gathered at an in vivo end of the blood gas probe. After a bolus of blood gas has been gathered, the bolus is extracted from the blood gas probe through the use of a vacuum extraction technique. The bolus of blood gas is then monitored in an ex vivo monitor or analyzer.
Both of these conventional techniques have significant disadvantages. First, both techniques rely on taking a sample from the system being analyzed. By definition, such an analyzing or monitoring technique is noncontinuous. Instead, such a technique provides merely a snapshot of the level of blood gas which existed in the system at the time the sample was taken.
Further, depending on where the blood sample or gas sample is analyzed, such techniques can introduce a significant delay. For example, in situations where a blood sample is drawn and analyzed in a lab, it can be 30 to 40 minutes, or even longer, before the physician obtains the results of the analysis. This can introduce a significant delay in providing necessary or desired treatment to the patient.
Also, in systems where a blood sample is drawn from a patient, the blood sample can easily become exposed to the exterior atmosphere. This allows some of the blood gases to diffuse into the gaseous state and other gases to diffuse into the blood sample prior to analysis. Such unwanted diffusion introduces inaccuracies in the results eventually obtained by analysis.
In addition, both techniques involve removing a sample from the system under analysis. The first technique involves removing an actual blood sample, while the second technique involves removing a sample of blood gas. Any time a sample is removed from the system under analysis, the system is altered. Altering the system under analysis introduces further inaccuracies into the results eventually obtained.
Further, in some instances in which arterial blood gas of a patient is being monitored, there has already been significant blood loss (e.g. in neonates) from the patient. In other instances, blood movement through the arterial system is sluggish. Thus, removal of a sample of either blood or blood gas presents the significant dangers of deleteriously depleting the blood or blood gases available for analysis.
Work has also recently been done in attempting to insert the actual blood gas sensors into the artery so they are in contact with the blood to be analyzed. However, such systems have encountered significant problems. First, such sensors are, of necessity, extremely small. Therefore, the sensors only measure blood gas from a very small amount of blood which actually contacts the sensors. In addition, with the sensors actually introduced into the artery, there has been found no effective way of calibrating the sensors. Thus, it is difficult to obtain any meaningful measurement from the sensors.